Noise has been a customer satisfaction issue associated with the commercial airline industry since the introduction of the aero turbine engine. One of the noise generation sources is associated with the rotating turbo machinery itself, as the result of rapidly rotating blade rows disposed within the air/gas stream. For example, in modern aeroengines high speed compressors have very high rotor tip speeds and a relative tip Mach number greater than 1. The noise propagated forward through the inlet duct of such aeroengines is mainly due to flow interactions between the rotor and variable inlet guide vanes (IGVs) positioned in the inlet duct upstream of the rotor for guiding incoming airflow in a desired direction toward the rotor. Considerable effort has been directed toward quieting aeroengines. For example, noise absorbing materials, perforated buffer plates and other noise attenuation devices have been used in aeroengines for suppressing noise propagation through the engines.
Accordingly, there is a need for an improved method and apparatus for reducing the noise generated by aero turbine engines.